1. Field of the Invention
The present invention relates to a method and equipment for measuring the internal structure of a composite material filled with ceramic particles having an irregular matrix. In more particularly, it relates to a method in which the internal structure (packing structure or dispersion condition of the particles) of a composite material filled with ceramic particles obtained by mixing raw ceramic particles into a liquid material is measured by making this visible and observing it by utilizing the photoelasticity based on local rearrangement of liquid material molecules, or the difference of refractive index of the particles and liquid material, and to an evaluation device used therein.
2. Description of the Related Art
Composite materials filled with ceramic particles are employed as insulating materials, electrode/conductive materials, electroviscous fluids, chemical/mechanical grinding slurries, and raw materials for ceramic molding processes such as injection molding and/or cast molding, and also, in recent years, have come to be widely used in sealing materials intended for protecting and insulating semiconductor elements. With progress in VLSI, in order to achieve increased element fineness, low viscosity/high forming ability of composite material filled with ceramic particles in order to achieve the ability to produce any required shape and/or to enable pouring between minute electrodes is indispensable.
However, scientific study of the field of such materials is still in its infancy and studies relating to the viscosity and moldability of composite material filled with ceramic particles are based merely on experience. For example, it means that lower viscosity of the composite is sought to be achieved by making the particle size distribution of the particles to be filled larger or by making the particle size of the particles larger. It has been pointed out that there are limits to the extent to which it is possible to achieve the accuracy required in for example semiconductor sealing materials simply using such conventional discoveries (for example, Shinsuke Hagiwara xe2x80x9cThe present state of development of semiconductor sealing materialsxe2x80x9d, Plastics, Vol. 49, p. 58, 1998 and Takeshi Kitano xe2x80x9cRheological properties of molten polymer solution filled with fillerxe2x80x9d, Filler, Vol. 3, p. 96, 1998).
A typical method of xe2x80x9cdirectlyxe2x80x9d evaluating the distribution condition of a particular material filled/dispersed in a composite material is the method in which some of the dispersed material is collected and its surface is polished and the reflected image thereof is observed by using an optical microscope or scanning electron microscope (SEM). For example, Laid-open Japanese Patent Publication Number 10-292055 (1998) discloses the former method using an SEM and in Laid-open Japanese Patent Publication Number 9-302210 (1997) an optical microscope method is applied to evaluation of uniformity of particle dispersion. However, with such methods, there is the risk of altering the distribution condition of the particles by the surface processing and, in addition, the information obtained is restricted to that from the reflection surface of the light from the light source i.e. to 2-dimensional information, so the distribution condition of the particulate material could not be evaluated directly over a wide region.
As a method of direct evaluation similar to the above, there is the method of observing the transmitted image by producing a thin strip of thickness capable of transmitting light from the light source. For example, Laid-open Japanese Patent Publication Number 61-122543 (1986) and Laid-open Japanese Patent Publication Number 5-232010 (1993) disclose methods using the transmitted image obtained by an optical microscope. With these methods, the problem of adverse effects due to processing and 2-dimensional observation is solved. In fact, by means of these methods, it is possible to recognize the packed particulate material itself. However, by using these on their own it is not possible to evaluate the bonding condition at the interface between the particles and the resin or the coagulation condition that is secondarily constituted within the interior of the dispersion system by the particles. The dominant factors in regard to rheological properties of a resin polymer composite filled with particles, which are currently becoming even more vital, are considered to be interactions at the particle/resin interface and the resin constituents within coagulations thereof. Evaluation of these is indispensable but, with previous methods, as will be described in detail with reference to the examples below, it has not been possible to achieve this.
As a method of evaluating a composite filled with particles in comparatively large volume that supplemented the defects of the reflection observation method, there was the method of indirectly deducing the distribution condition of the particulate material by measuring for example the coefficient of viscosity, electrical resistance or tensile strength of the dispersion system. For example, Laid-open Japanese Patent Publication Number 6-229984 (1994) and Laid-open Japanese Patent Publication Number 11-64260 (1999) are examples of a method of measuring electrical resistance and Laid-open Japanese Patent Publication Number 10-311783 (1998) is an example of a method of measuring tensile strength. Even such methods were insufficient to obtain local information such as the interactions at the particle/resin interface or the particle coagulation structure.
One cause of the above problem is considered to be that no method has been established for observing the internal structure of a dispersed system and correlating this with mechanical properties/rheological properties/electrical properties etc. of the dispersion system in cases where the liquid material is a matrix or dispersion medium. For example, one problem is considered to be that no methodology has been established for the application of methods of measurement using an optical microscope or scanning electron microscope (SEM), which are universal in regard to dispersion systems where the dispersion medium of the particulate material is solid (for example ceramic material systems) to composite material filled with particles having an irregular matrix. Even where the matrix is a solid dispersion system, studies based on such a viewpoint have only just been commenced.
Conventionally, in addition to the risk of altering the distribution condition of the particles by surface processing methods using an SEM, the information obtained was restricted to the reflection surface of the light from the light source i.e. was only 2-dimensional information and so could not be used to evaluate the distribution condition of the particulate material directly in a region. In this regard, a method has been proposed for performing evaluation using transmission images utilizing the difference of refractive index etc. at the interface between particulate material and gas bubbles contained within the dispersion system (K. Uematsu, xe2x80x9cImmersion microscopy for detailed characterization of defects in ceramic powders and green bodiesxe2x80x9d, Powder Technology, Vol. 88, p. 291, 1996). With this method, the problems of adverse effects due to processing and 2-dimensional observation are solved. Establishment of a similar method for evaluation in regard to liquid materials filled with particles is indispensable.
The case when the liquid material in a liquid material filled with particles.dispersion system is a resin-based material can be regarded as one type of polymer material. In polymeric material systems, typically use is made of polarized light observation for evaluation of the photoelasticity characteristic with applied stress, measurement of the birefringence of a plastic lens, or evaluation of molecular alignment characteristics in liquid crystal materials. However, previously, no attempts have been made to employ this for evaluation of the characteristics of particles, rather than resin, in resin filled with particles.dispersion materials. The reason for this is believed to be that the particulate materials that are generally employed in this material field are (amorphous) SiO2 particles and it was not intuitively anticipated that these methods of observation could be applied to materials having an isotropic crystalline structure (or not having a crystalline structure).
In order to overcome the defects possessed by such conventional measurement techniques for composite materials filled with particles, the present invention was developed taking as technical problem the provision of a method of measurement of the internal structure (packing structure or dispersion condition of the particulate material) of particulate material in the composite materials and evaluation equipment employing this principle of measurement by visualization and observation utilizing the photoelasticity based on local rearrangement of liquid molecules and the difference of refractive indices of the particulate material and liquid material.
The inventors have noted an evaluation technique for photoelasticity or optical anisotropy that is conducted with polymeric materials. Specifically, the present inventors, having in mind that, in preparing a composite material filled with particles, if the packing structure of the particulate material was non-uniform or secondary coagulations were created, this would apply stress to the surrounding liquid material, increasing the alignment of polymer molecules etc. compared with locations where this did not apply, and would generate gas bubbles at interface regions of the particulate material and liquid material, or that the interface itself (connected surface comprising different refractive indices) comprising materials of different kinds would constitute an optically anisotropic body, and that these would have optical distortion enabling them to be evaluated by diagonal position observation, as a result of meticulous study aimed at implementing the above concept and various studies concerning the primary properties of particles such as particle size distribution of the particulate material serving as filler and the effect of method of preparation and the condition of the evaluation sample, discovered that the packing structure and/or dispersion condition of the particulate material could be identified by using such optical anisotropy and perfected the present invention based on this discovery.
A method of measuring the internal structure (packing structure or dispersion condition of the particulate material) of a composite filled with particles, wherein the drawbacks possessed by the conventional measurement technique for composite materials filled with particles are ameliorated. This invention relates to a method of measuring the internal structure (packing structure or dispersion condition of particulate material) of a composite filled with particles having an irregular matrix by observations based on its optical anisotropy, in which the internal structure (packing structure or dispersion condition of particulate material) of the composite obtained by mixing particulate material as raw material with a liquid material is made visible by utilizing the photoelasticity based on local rearrangement of liquid material molecules or difference of refractive indices of the particulate material and liquid material, and the structure thereof are observed, and an evaluation device using this principle of measurement. This makes it possible to provide a technique or evaluation device for observing the internal structure (packing structure or dispersion condition of particulate material) of a composite filled with particles wherein the liquid material is a matrix or dispersion medium, and in particular is ideal as a technique for structural analysis or a technique for manufacturing process control of insulating materials or semiconductor sealing materials in which there is a great need to identify the internal structure.
An object of the present invention is to provide a method and evaluation equipment used therein for measuring the internal structure constituted by the packing structure and/or dispersion condition of the particulate material in a composite material filled with particles having an irregular matrix obtained by mixing a particulate material as raw material with a liquid material by utilizing the photoelasticity effect of the liquid material and/or the optical anisotropy etc. possessed by the particle/liquid interface.
In order to realize the above object, according to the present invention, the following constitution is adopted:
(1) A method of measuring the internal structure (packing structure or dispersion condition of particulate material) of a composite material filled with ceramic particles having an irregular matrix by observations based on its optical anisotropy, which comprises mixing particulate material as raw material with a liquid material to obtain a composite material filled with ceramic particles, making visible the internal structure (packing structure or dispersion condition of particulate material) of the composite material by utilizing the photoelasticity based on local rearrangement of liquid material molecules or difference of refractive indices of the particulate material and liquid material, and then observing the structure.
(2) The method of measuring the internal structure of a composite material filled with ceramic particles according to (1) above, wherein the particulate material is an SiO2 based material or AlN based material.
(3) The method of measuring the internal structure of a composite material filled with ceramic particles according to (1) above, wherein the liquid material is a resin based material.
(4) Equipment for evaluation used in the method of measurement claimed in any of (1) to (3) above, which comprises as structural elements two polarizing elements, a light source or electron beam source, means for observing a transmitted image, and means for arranging a sample, wherein a thin strip sample for transmission observation is arranged between the two polarizing elements, monochromatic light polarized by the first polarizing element is directed onto the sample, and subjected to double refraction at optically anisotropic regions such as coagulations in the sample, then re-polarized by the second polarizing element, and observed by the transmitted image observation means to evaluate optical behavior thereof such as diagonally opposite positions or interference.
(5) The evaluation equipment according to (4) above, wherein the sample is a composite material filled with particles converted to the form of a thin strip of a thickness allowing monochromatic light from a light source or electron beam source to be transmitted through the composite material.
(6) The evaluation equipment according to (4) above, wherein halogen light is directed on the sample.